1. Field of the Invention
The present invention relates to a position detecting device for detecting a position designated by a position designating magnetic generator on the basis of a change in magnetic permeability of magnetic elements to which a magnetic field is applied by the magnetic generator.
2. Description of the Related Art
A typical conventional position detecting device is arranged such that a driving coil is provided either at one end of a magnetostrictive transmission medium or at the distal end of a position designating pen, while a detecting coil is provided on the other of the two, and a pulsating current is applied to the driving coil so as to cause the transmission medium to generate a magnetostrictive oscillatory wave which in turn causes a voltage corresponding thereto to be induced in the detecting coil. The period of time beginning at the time when the oscillatory wave is generated and ending at the time when the induced voltage is detected is measured by a processor or other similar means, and the position designated by the position designating pen is calculated on the basis of the measured period of time. This device has a relatively high degree of accuracy in position detection, but suffers from the following problems. Namely, since a timing signal and the like are transferred between the pen and the processor or the like, a cord is needed to connect the pen and the device, which remarkably limits the range within which the pen can be handled. In addition, the cord is easily affected by induction caused by external devices, which leads to an erroneous operation and also involves a risk of the cord becoming a noise generating source. Further, the conventional device requires the pen to be held perpendicular with respect to the plane of the magnetostrictive transmission medium and in close proximity with the surface of the transmission medium when a position is designated using the pen.
There is another conventional position detecting device wherein a plurality of driving lines and a plurality of detecting lines are disposed orthogonally with respect to each other, and the driving lines are successively supplied with a current, while the detecting lines are successively selected in order to detect voltages induced therein, whereby a position designated by a position designating pen having a magnetic material such as ferrite is detected from the position of the detecting line having a relatively large induced voltage. This device enables the position designating pen to be cordless, but still suffers from the following problems. Namely, the resolution of coordinate positions is determined by the distance between each pair of adjacent lines, and if this distance is reduced in order to improve the resolution, then SN ratio and stability deteriorate. For this reason, it is difficult to improve the resolution. It is also difficult to detect the positions directly above the intersections between the driving and detecting lines. Further, the pen needs to be brought in close proximity with the lines, which makes it impossible to place a thick member on the input surface when the pen is used.